The Democrats have had an excellent week. On Tuesday, they not only seized the governorships of New Jersey and Virginia, they won a host of down-ballot contests, most notably for the Virginia House of Delegates. TheNew York Times' headline summarized succinctly the pattern to the GOP's rout: "Suburbs Revolt Against Trump."

Which has me a little worried. Not because I hoped the GOP would hold on to the suburbs: I want the Republicans to lose their majorities in both houses of Congress in 2018, along with control of a host of state legislatures and governorships, and losing the suburbs will help handily in making that day a reality. But I worry that this particular path to victory, far from transcending the toxic polarization that is crippling our democracy, will only turn that particular screw a bit tighter.

In very broad strokes, the two electoral coalitions that emerged in 2016 look something like the following. The Democrats dominate in urban areas, among non-whites and among more educated whites, particularly professional ones. Republicans dominate in more rural areas, among less-educated whites and among career military and business owners. The divide is more geographic, ethnic, and cultural than it is economic.

But that doesn't mean it doesn't have economic consequences. This kind of division, where groups of voters see themselves as fundamentally alienated from each other rather than interdependent, empowers the elite groups within each coalition to maximize their demands, because the great mass of voters perceive themselves as having no choice but to support their "side" no matter what. In this way, political polarization contributes to greater concentration of economic and political power in the hands of existing elites.

This turns out to be true even in the context of an apparent populist revolt. We've already seen this dynamic play out with the GOP tax cut bill, which, particularly with its elimination of the estate tax, is transparently aimed at benefiting the most rarified slice of the elite, in blatant contradiction of the Trump campaign's populist posturing. But while the bill is a huge windfall for the 0.01 percent, my colleague Jeff Spross has pointed out that many of the people it hurts are also among the elite — just not quite as elite. That turns out to be the bulk of the populist content: an attack on their elites, and an enrichment of ours.

Many of those people who stand to lose out under the GOP tax bill live in precisely the upscale suburbs that might flip to the Democrats in 2018. If that happens, the Democratic agenda going forward is likely to reflect a desire to retain the loyalty of these voters. And that's a problem.

I don't want to overstate my concern. As Matt Yglesias noted earlier this week, while Tuesday's map was relatively blue-friendly, Democrats didn't just improve their numbers in friendly places. They improved across the board, among older voters as well as younger, in Trump-voting districts as well Clinton-voting ones, and in some cases — like Michigan's upper peninsula — they improved their numbers dramatically enough to win by large margins in districts Trump won last year. And there's ample evidence that the party rank-and-file seek to push the party in a more populist direction economically.

But the Republican Party rank-and-file wanted a dramatic change of direction, too, and look what it got them. Meanwhile, if the axis of polarization deepens even as Democrats improve their performance across the board, then while Democrats will win in a few rural and overwhelmingly white areas, the bulk of their gains will come in wealthier and more ethnically diverse districts that are economically connected to urban centers. The party will — only rationally — come to conceive of the general interest more in terms of the interests of the voters they won rather than those it has less chance of winning. And in the next election cycle, the Republicans will have every incentive to respond in ways that deepen polarization further.

Either or both parties may be able to thrive in that kind polarizing cycle. For the sake of the country, we have to work to see they don't.